1. Field of the Invention
This invention generally relates to ceramic electronic packaging. Specifically, there is a multilayered ceramic package having a cavity with structural supports that is bonded to a micro-machined semiconductor device.
2. Description of the Related Art
Various devices and techniques are used for packaging of micro-machined semiconductor devices. Typically, a micro-machined semiconductor die is fabricated with wirebond pads and a sealing structure. A silicon lid has a cavity etched therein using a strong acid such as hydrofluoric. The micro-machined semiconductor needs space within the package to allow the moving surfaces of the device to function properly. The silicon lid can be attached to the semiconductor die by an adhesive. The die and lid assembly is placed on a hybrid ceramic where the bond pads on the die are wirebonded to bond pads on the hybrid ceramic. The hybrid ceramic is then encapsulated within a hermetic package. This package has several problems. First, wire bonds are fragile and are subject to being torn away during mechanical assembly of the package. Second, the ceramic hybrid is expensive to produce. Third, if one of the parts in the hybrid circuit is defective, the whole circuit has to be thrown away. Previous attempts at packaging micro-machined semiconductor devices have encountered difficulties in producing reliable electrical connections and hermetic seals that will survive environmental stress and be economically manufactured.
Typical micro-machined semiconductor structures contain metal elements on their surfaces which cannot be passivated through traditional glass passivation processes, however they still must be hermetically sealed. Current techniques include “attaching” a silicon lid, which has a cavity etched into its underside to clear the micro-machined structure, to the surface of the die exposing only the bonding pads. This configuration accomplishes the hermetic seal but will not allow for flip chip processes to be used as the die I/O pads cannot be brought to the surface.
An example of a micro-machined semiconductor package is shown in U.S. Pat. No. 6,225,692 to Hinds. The contents of which are herein specifically incorporated by reference. U.S. Pat. No. 6,225,692 has a semiconductor device that is attached by reflowing solder paste or plating to a low temperature co-fired ceramic (LTCC) package. A hermetic seal is obtained by a solder seal ring that is also reflowed. While this design has advantages, one disadvantage is that it is difficult to control the dimensions of the distance between the micro-machined semiconductor device and the package substrate. When the solder reflows, it can spread out resulting in uneven solder heights. Another disadvantage is that forming the cavity adds additional cost and processing steps.
Despite the advantages of the prior art designs, none have combined a highly reliable package with a design that is readily manufacturable at a low cost.